i was wondering which of these two would be cheaper piggy back or custom ecu flash.

 

Both create some issue and can't be answered so readily. I'm not so sure you'll be able to find someone in your area that can do custom programming on this computer. It will require the presence of the car, a dyno, and or lambda probe and a full day of work running the car under different conditions. If they have the programming language... $1,500 minimum.

I have yet to find a working, off-the-shelf piggyback system for the car. And everyone I have spoken with that is willing to try to build one is quoting somewhere in the range of $4,000 with no guarantees. Again, because they don't have the OEM software and do not know what problems they may run into...